A suicide attacker has blown up a tanker lorry at the police HQ in the Iraqi city of Tikrit, killing at least nine people, officials say.

A majority of the casualties and injured are thought to have been police officers, AFP news agency reports.

The city, which lies 160km (100 miles) north of the capital Baghdad, was the hometown of ex-leader Saddam Hussein.

Violence has decreased in Iraq since the peak of the insurgency in 2006 and 2007, but bombings are still common.

Sunni Islamist militants linked to al-Qaeda have vowed to step up attacks on Shia and official targets this year, in an attempt to weaken the Shia-led government.

Last week, at least 19 people died and more than 100 were wounded in a spate of car bomb attacks in the northern city of Kilkurk. March saw 271 people killed in attacks across Iraq - the highest death toll for six months.

Political crisis

Monday's blast, inside a compound housing various government offices in central Tikrit, left a huge crater and damaged many nearby buildings.

Police say the vehicle may have got through security because it appeared to be a truck making a regular delivery of oil and gas.

The violence comes ahead of provincial elections scheduled to take place on 20 April, as a long-running crisis between Shia and Sunni political leaders shows no sign of easing.

Tensions, especially in Sunni regions of the country, have been exacerbated by the efforts of Iraq's Shia Prime Minister Nouri al-Maliki to tighten his grip on power, says the BBC's diplomatic correspondent, Jonathan Marcus.

With the influential Iraqi President, Jalal Talabani - a Kurd - out of action having suffered a stroke, there are renewed fears the country could split along sectarian and ethnic lines, adds our correspondent.